Which of the following reaction is possible at anode ?

Options

A. `2Cr^(3+) + 7H_2O to Cr_2O_7^(2-) + 14 H^+`
B. `F_2 to 2F^-`
C. `(1//2)O_2 + 2H^(+) to H_2O`
D. None of these

Answer

To determine which of the given reactions is possible at the anode, we need to remember that the anode is the electrode where oxidation occurs. Oxidation is defined as the loss of electrons. Let's analyze each of the options provided to identify which reaction involves oxidation.

### Step-by-Step Solution:

1. **Understand the Role of Anode**:
- The anode is the electrode where oxidation takes place. Oxidation involves the loss of electrons.

2. **Analyze Each Reaction**:
- **Option 1**: \( 2 \text{Cr}^{3+} + 7 \text{H}_2\text{O} \rightarrow \text{Cr}_2\text{O}_7^{2-} + 14 \text{H}^+ \)
- In this reaction, the chromium ions (\( \text{Cr}^{3+} \)) are being converted into dichromate ions (\( \text{Cr}_2\text{O}_7^{2-} \)).
- To balance the charges, we see that the total charge on the products is \( +14 \) (from \( 14 \text{H}^+ \)) and \( -2 \) (from \( \text{Cr}_2\text{O}_7^{2-} \)), giving a total of \( +12 \). The reactants have a total charge of \( +6 \) (from \( 2 \text{Cr}^{3+} \)).
- This indicates that \( 6 \) electrons are released, confirming that this is an oxidation reaction. **Thus, this reaction is possible at the anode.**

- **Option 2**: \( \text{F}_2 + 2 \text{e}^- \rightarrow 2 \text{F}^- \)
- Here, fluorine (\( \text{F}_2 \)) is gaining electrons to form fluoride ions (\( \text{F}^- \)).
- Since this reaction involves the gain of electrons, it is a reduction reaction. **Thus, this reaction occurs at the cathode, not the anode.**

- **Option 3**: \( \text{H}_2 + 2 \text{H}^+ \rightarrow 2 \text{H}_2\text{O} + 2 \text{e}^- \)
- In this case, hydrogen gas (\( \text{H}_2 \)) is reacting with protons (\( \text{H}^+ \)) to form water.
- This reaction also involves the gain of electrons, indicating that it is a reduction reaction. **Thus, this reaction also occurs at the cathode, not the anode.**

3. **Conclusion**:
- After analyzing all the options, we find that only **Option 1** represents an oxidation reaction, which is possible at the anode.

### Final Answer:
**The reaction that is possible at the anode is Option 1: \( 2 \text{Cr}^{3+} + 7 \text{H}_2\text{O} \rightarrow \text{Cr}_2\text{O}_7^{2-} + 14 \text{H}^+ \)**.